Nanoblocks are basically Legos except that 4 dots fit in the space of 1 Lego dot, and their undersides are channels so that (alas) pieces can slide around. The instructions are also top-down, one layer at a time, which I usually find easier than Lego instructions. I really like building their more complicated sets; last summer I did Himeji Castle (photo album) for my birthday, and this Christmas I got a deluxe edition bonsai pine, which I finished tonight. Here's the photo album.
(Edit: elsewhere someone said the next step was putting teeny elvish buildings on the branches and boy, I wish I could!)
After I took a picture of the bonsai next to Himeji Castle, I immediately started disassembling the castle. This is probably kind of weird, but we have enough clutter as it is, and the pleasure is largely in the assembly—and this way I can re-assemble sometime if I like.
If you do the more intricate Nanoblock sets, by the way, I recommend the special tweezers, mostly for getting pieces apart that you've put in the wrong place.